Bo Qin - Aspects and Consequences of a New Initiation Mode of Bacterial Ribosomes, the 70S-Scanning Initiation

Protein synthesis occurs in all cells and can be divided into four phases: Initiation, elongation, termination and recycling, which are governed by special factors. It is textbook knowledge that in bacteria the small ribosomal 30S subunit recognizes the initiation signals of an mRNA and after association with the large ribosomal 50S subunit enters as 70S ribosome the elongation phase. We detected a novel initiation mode in our working group, the 70S-scanning initiation, where the 70S ribosome does not necessarily dissociate after translation of a cistron, but rather scans to the initiation site of the downstream cistron. This mode accounts for about 50% of all initiation events in E. coli. The idea that 70S scan the mRNA for initiation signals after terminating the synthesis of a protein is in conflict with another textbook wisdom, according to which a 70S ribosome separates into its subunits after termination with the help of the “ribosome recycling factor” RRF and EF-G. In fact, the recycling phase is considered as the fourth functional phase after termination. This apparent balance was analyzed in our working group.